(a) Field of the Invention
The invention relates to a video telephone integrating public-switch telephone network (PSTN) and asymmetric digital subscriber line (ADSL), and more particularly, to a phone device capable of bi-directional video and audio transmissions using conventional telephone lines (double-twist lines). Not only is PSTN, which serves as a telephone system for analog audio signals using copper wires, utilized for providing audio transmissions as common telephones, but also a high frequency band ranging from 25 KHz to 1 MHz of ADSL is used for accomplishing video information transmissions. Through a connection established by the PSTN, Internet protocol (IP) addresses and port addresses are transmitted in any form via the PSTN, including those of a receiving party to a calling part, and those of a calling party to a receiving party. Digital information is then transmitted via the Internet, thereby completing simultaneous and bi-directional video and audio transmissions between the receiving party and the calling party.
At the same time when using the Internet for transmissions, the PSTN may be disconnected or left connected.
Or, the PSTN may be employed for establishing an initial connection, and the Internet is then used for transmitting audio and video information between the receiving party and the calling party.
(b) Description of the Prior Art
Present analog public-switch telephone network (PSTN) plays a leading role in digital communications for being most complete in structure, and being most extensively used as well as inexpensive in price. In addition, the Internet that is rapidly advancing during the recent years, especially the world-wide-web (www), apart from offering conventional email transmissions, also realizes diverse multimedia services combining audio, graphics, and even dynamic video images. Thus, massive data are brought about along with these services. In order to acquire data accessing capabilities with higher transmission speeds, Internet service providers (ISP) have one after another proposed various schemes for increasing transmission speeds. As multimedia on the Internet gets more and more popular, it is only apparent that modems of 28.8, 33.6 or 56 kbps using conventional dial-up telephone networks become inadequate for users to keep up with the trend. Even, users of local networks and integrated system digital networks (ISDN) hardly consider speeds of their existing networks as satisfactory either.
Meanwhile, ˜digital subscriber line (xDSL) is gradually turning into a target attention of the public. Literally, DSL is a kind of digital subscriber line, with asymmetric digital subscriber line (ADSL) being one of the most prominent xDSL techniques. The ADSL utilizes the contemporary PSTN (or, plain old telephone service, POTS) to transmit data in high transmission speeds without requiring augmentation of existing fundamental structural equipments and techniques. Related standards of ADSL have been established, and the ADSL is certainly to bring people considerable benefits. Again, ADSL literally means asymmetric digital subscriber line; that is to say, a high frequency band ranging from 30 KHz to 1 MHz over common telephone lines (copper telephone lines in households), is not overlapped with a low frequency band occupied by telephone audio signals. Therefore, both audio signals and data can be simultaneously transmitted for increasing transmission speeds.
Because ADSL utilizes present PSTN (POTS) lines for transmitting data with high transmission speeds, functions of conventional telephones are essential. Within a bandwidth of 1 MHz, a lowest bandwidth of 4 KHz (0 to 4 KHz) is adopted for conventional telephone services. This bandwidth of 4 KHz is separated by a passive filter called a POST splitter from the bandwidth of 1 MHz, and is especially reserved and tailored for conventional telephone services. The remaining portion from 100 KHz to 1.1 MHz then transmits computer data at a speed of 6 bits per second. Moreover, because a power supply that sends ADSL signals and POTS signals on a same line is provided by a telecommunication provider, the power supply is still available even if when the ADSL line malfunctions or a personal computer is shut down. Therefore, a user may still make phone calls using POTS channels by separating audio signals from ADSL signals. The ADSL separates conventional telephone services and computer data services to different channels, and hence it is ensured that telephone services function normally in cases of malfunctions or interruptions of ADSL services. To be more precise, telephones are able to function normally when multimedia transmissions are being performed via the ADSL.
Above all, owing to launches of various related products, communication bandwidths of the PSTN have been directly improved and user demands of PSTN have been indirectly lowered. Also, popularity of newly promoted communication networks are to remain quite limited in the near future, and thus the PSTN still stands as the mainstream among data communication networks.